A multiple access mobile communication system enables a plurality of wireless terminals to perform radio communication substantially simultaneously, by sharing radio resources including at least one of time, frequency, and transmission power among the plurality of wireless terminals. Typical examples of multiple access schemes include TDMA (Time Division Multiple Access), FDMA (Frequency Division Multiple Access), CDMA (Code Division Multiple Access), OFDMA (Orthogonal Frequency Division Multiple Access), and any combination thereof.
The term “mobile communication system” used in the present specification refers to a multiple access mobile communication system unless otherwise specified. A mobile communication system includes wireless terminals and an upper network. The upper network includes base stations, relay nodes that relay traffic, and control nodes that perform radio resource management, mobility management, bearer management and the like.
When new downlink traffic (downlink data or incoming voice) to a wireless terminal in a standby state has arrived at an upper network, the upper network transmits a paging signal to the wireless terminal. The wireless terminal in the standby state performs a discontinuous reception (DRX) in order to receive a paging signal. Then the wireless terminal initiates, in response to reception of the paging signal addressed thereto, signaling to establish communication for receiving the downlink traffic. This signaling includes a response message to the paging. The response message includes one or both of a request for establishing a control connection and a service request for establishing a communication path (a bearer) that transfers user-data. In response to the response message, the network executes procedures for configuring the control connection and the communication path (bearer) required for transmitting the downlink traffic to the wireless terminal.
Note that, in paging a wireless terminal, an upper network needs to determine an area to which a paging signal is sent. In the present specification, the area to which a paging signal is sent is referred to as “the paging area”. The paging area includes at least one cell, and generally includes a plurality of cells (or sectors). Typically, the paging area agrees with the latest location registration area to which the wireless terminal belongs. The location registration area is a management unit in the upper network of the wireless terminal in the standby state. The location registration area includes one or a plurality of cells. When the wireless terminal crosses over from one location registration area to another, the wireless terminal sends a location update message to the upper network. Further, the wireless terminal may periodically sends a location update message irrespective of occurrence of any change in the location registration area.
For example, in a packet exchanged domain of 3GPP (the 3rd Generation Partnership Project) UMTS (Universal Mobile Telecommunications System), a location registration area is referred to as a routing area (RA). Accordingly, paging of a wireless terminal in the standby state (CELL_PCH state or URA_PCH state) is generally performed by broadcasting a paging signal in the RA.
Further, in 3GPP EPS (Evolved Packet System) or LTE (Long Term Evolution), a location registration area is referred to as a tracking area (TA). Further, in the EPS, a wireless terminal can be assigned a plurality of TAs. Specifically, on the occasion of an initial attach or tracking area update (TAU: Tracking Area Update) of a wireless terminal, the wireless terminal is notified of a TA list including one or a plurality of TAs. Thus, a TA list is a unit of location management of a mobile terminal. Accordingly, paging of a wireless terminal in the standby state (RRC_IDLE (ECM_IDLE) state) is generally performed by broadcasting a paging signal in all the TAs included in the TA list.
Patent Literatures 1 and 2 disclose techniques of narrowing a paging area as compared to the general location registration area through use of a movement history of a wireless terminal. By narrowing a paging area, the paging load of a mobile communication system can be reduced.
Patent Literature 1 discloses calculating a movement distance (i.e., a moving speed) of a wireless terminal per unit time using a history of location update messages sent from the wireless terminal, and determining, as the paging area, base stations included in a circle whose radius is the calculated movement distance.
Patent Literature 2 discloses performing location management of a wireless terminal using not only location update messages but also location information by means of a GPS (Global Positioning System). The method disclosed in Patent Literature 2 includes determining, in the case where the latest location information of a wireless terminal received by the upper network is GPS location information, the paging area of a limited range as compared to the location registration area based on the GPS location information. Further, Patent Literature 2 discloses calculating a moving speed of a wireless terminal using a history of location update messages and that of GPS location information, and enlarging the paging area as the moving speed of the wireless terminal becomes faster. Specifically, in order to enlarge the paging area, an identifier for specifying the paging area is changed in order of a sector identifier, a radio network controller (RNC) identifier, and a RAI (Routing Area Indicator).
Patent Literature 3 discloses determining a paging area of a wireless terminal in accordance with a communication state (e.g., communication quantity) or an operating state (e.g., movement frequency) of the wireless terminal. Specifically, the wireless terminal disclosed in Patent Literature 3 monitors its communication state (e.g., communication quantity) and operating state (e.g., movement frequency), and sends a control packet (paging request packet) to a core network. The core network in Patent Literature 3 receives the control packet (paging request packet) from the wireless terminal, and determines the paging area of the wireless terminal in accordance with the communication state or operating state thereof indicated by the control packet.
Patent Literature 4 discloses that a base station determines a mobility state of a wireless terminal, and determines a tracking area (TA) to be assigned to the wireless terminal based on the determined mobility state. For example, in an architecture in which a wireless terminal can be assigned a plurality of TAs, the network assigns one TA to a wireless terminal in a stationary state or a low mobility state, and assigns a plurality of TAs to a wireless terminal in a high mobility state. Alternatively, in an architecture where a cell can belong to a plurality of TAs, the network assigns a TA that covers a small geographical area to a wireless terminal in the stationary state or the low mobility state, and assigns a TA that covers a large geographical area to a wireless terminal in the high mobility state. Further, Patent Literature 4 discloses, for the purpose of determining the mobility state of a wireless terminal, use of at least one of: (a) a measured value of the number of tracking area updates (TAUs) of the wireless terminal; (b) a measured value of the number of cell reselections executed by the wireless terminal; and (c) measurement results of a position (e.g., longitude and latitude) of the wireless terminal. Note that, in Patent Literature 4, a TA and a paging area are in a one-to-one correspondence with each other, and paging of a wireless terminal is performed on one or a plurality of TAs assigned to the wireless terminal.
Patent Literature 5 discloses a communication method including the following steps (a) to (c):
(a) sending, from the wireless terminal to a communication network, an indicator explicitly indicating that a wireless terminal (typically an M2M (machine-to-machine) device) is in low mobility;
(b) informing, by the wireless terminal, the communication network about a location (typically a sector) of the wireless terminal; and
(c) sending a paging message to an area limited to the location (typically a sector) informed by the wireless terminal.